The present invention is generally related to methods, devices, and systems for controlling surgical fluid flows, particularly during treatment of an eye. In exemplary embodiments, the invention removes material from within the eye in part by a displacement-induced aspiration flow (such as that caused by a peristaltic or other positive displacement pump), and in part by a vacuum-induced aspiration flow (such as that caused by a venturi pump). Optionally, the aspiration flow may switch between a displacement pump and a venturi pump while material is being fragmented and removed from within the eye. While the system operator will typically have control over the overall mode of operation throughout a procedure, switching between these two different types of aspiration flow may occur “on-the-fly” without halting of a corresponding irrigation flow, and without awaiting input from the system operator regarding that particular flow change. The material may be removed from an anterior or posterior chamber of the eye, such as for phacoemulsification of cataracts, treatment of retinal diseases, vitrectomy, and the like.
The optical elements of the eye include both a cornea (at the front of the eye) and a lens within the eye. The lens and cornea work together to focus light onto the retina at the back of the eye. The lens also changes in shape, adjusting the focus of the eye to vary between viewing near objects and far objects. The lens is found just behind the pupil, and within a capsular bag. This capsular bag is a thin, relatively delicate structure which separates the eye into anterior and posterior chambers.
With age, clouding of the lens or cataracts is fairly common. Cataracts may form in the hard central nucleus of the lens, in the softer peripheral cortical portion of the lens, or at the back of the lens near the capsular bag.
Cataracts can be treated by the replacement of the cloudy lens with an artificial lens. Phacoemulsification systems often use ultrasound energy to fragment the lens and aspirate the lens material from within the capsular bag. This may allow the remaining capsular bag to be used for positioning of the artificial lens, and maintains the separation between the anterior portion of the eye and the vitreous humour in the posterior chamber of the eye.
During cataract surgery and other therapies of the eye, accurate control over the volume of fluid within the eye is highly beneficial. For example, while ultrasound energy breaks up the lens and allows it to be drawn into a treatment probe with an aspiration flow, a corresponding irrigation flow may be introduced into the eye so that the total volume of fluid in the eye does not change excessively. If the total volume of fluid in the eye is allowed to get too low at any time during the procedure, the eye may collapse and cause significant tissue damage. Similarly, excessive pressure within the eye may strain and injure tissues of the eye.
While a variety of specific fluid transport mechanisms have been used in phacoemulsification and other treatment systems for the eyes, aspiration flow systems can generally be classified in two categories: 1) volumetric-based aspiration flow systems using positive displacement pumps; and 2) vacuum-based aspiration systems using a vacuum source, typically applied to the aspiration flow through an air-liquid interface. Among positive displacement aspiration systems, peristaltic pumps (which use rotating rollers that press against a flexible tubing to induce flow) are commonly employed. Such pumps provide accurate control over the flow volume. The pressure of the flow, however, is less accurately controlled and the variations in vacuum may result in the feel or traction of the handpiece varying during a procedure. Peristaltic and other displacement pump systems may also be somewhat slow for some procedures. Vacuum rise times tend to be slower for peristaltic systems than venturi systems. This may result in an overall sluggish feel to the surgeon. Moreover, the ultrasonic vibrations of a phacoemulsification tip may (despite peristaltic aspiration flow into the tip) inhibit the desired fragmentation-inducing engagement between the tip and tissue particles.
Vacuum-based aspiration systems provide accurate control over the fluid pressure within the eye, particularly when combined with gravity-fed irrigation systems. While vacuum-based systems can (in some circumstances) result in excessive fluid flows, they may have advantages when, for example, it is desired to bring tissue fragments to the probe, or when removing a relatively large quantity of the viscous vitreous humour from the posterior chamber of the eye. Unfortunately, venturi pump and other vacuum-based aspiration flow systems are subject to pressure surges during occlusion of the treatment probe, and such pressure surges may decrease the surgeon's control over the eye treatment procedure. Displacement pump systems are similarly subject to vacuum spikes during and immediately following occlusion of the probe.
While there have been prior proposals for multiple pump systems which make use of either a positive displacement pump or a vacuum source, the previously proposed systems have not been ideal. Hence, to provide surgeons with the benefits of both vacuum-based and displacement-based aspiration flows, still further improvements appear desirable. In particular, interrupting a procedure to switch between aspiration systems may be inconvenient, and it may be difficult or even impossible to take full advantage (for example) of the full potential of combining both vacuum-based and displacement-based aspiration flows using prior eye treatment systems.
In light of the above, it would be advantageous to provide improved devices, systems, and methods for eye surgery. It would be particularly advantageous if these improvements allowed system users to maintain the benefits of vacuum and/or displacement fluid control systems when appropriate, and without having to interrupt the procedure to manually switch pumps, change handpieces or other system components, or the like. Ideally, these improved systems would provide benefits beyond those of peristaltic or venturi systems alone, such as combination peristaltic/venturi systems, without delaying the procedure or increasing the complexity of the operation to the system operator.